Previous work has demonstrated that well differentiated human endothelial cells (ECs) will self assemble into vascular conduits in protein gels both in vitro and in vivo after implantation into immunodeficient mouse hosts. Vessel maturation in grafts containing only EC requires recruitment of host mural cells, such as vascular smooth muscle cells or pericytes (PCs). The maturation of vessels is accelerated and enhanced when ECs are co-implanted with human PCs. Vessel self assembly can also be enhanced by sustained delivery of pro- angiogenic proteins that act on ECs or PCs, especially when an EC-directed agent, vascular endothelial growth factor (VEGF), is combined with a PC-directed agent, monocyte chemotactic protein -1 (MCP-1). However, vessel self-assembly and maturation still appears too slow to optimize parenchymal cell survival, requiring at least 10 days. The actions of pro-angiogenic proteins may be augmented or limited by positive and negative feedback loops, respectively, within the target cells that involve microRNAs (miRNAs). miRNAs are short, non-coding RNAs that regulate a variety of development processes by reducing specific mRNA half lives or translation. A single miRNA can reduce the expression of multiple genes often in the same pathway. The effects of miRNAs can be inhibited by complementary short RNA sequences referred to as antagomirs. Antagomirs act in a cell-specific manner when the miRNA is expressed in a cell specific manner. This project tests the hypothesis that controlled delivery of an antagomir can enhance the therapeutic benefits of angiogenic proteins such as VEGF in vascular self-assembly. This hypothesis will be tested through two specific aims. In Aim 1, polymer nanoparticles (NP) will be used to find the optimal approaches for providing spatial and temporal control over miRNA and antagomir delivery to the cytoplasm of ECs in 3D culture. In Aim 2, these NP delivery systems will be tested for their ability to control the spatial and temporal delivery of antagomirs to miR-17/20-which is known to augment the effects of VEGF-to 3D cell cultures produced by suspending ECs and PCs in gels of collagen and fibronectin. (End of Abstract)